(1) Field of the Invention
The present invention relates to an improved spin trimming apparatus particularly for a blow molded container. In particular, the present invention relates to a spin trimming apparatus for removing an upper dome scrap from a hollow, blow molded plastic container, such as a plastic bottle. The spin trimming apparatus is comprised of a pair of rotating belts mounted above and on opposite sides of a conveyor for the bottle. The bottle is placed on the conveyor in an upstanding position, upstream from the trimming apparatus and the conveyor feeds the bottle into a chute comprised of opposed rails that mate with an annular groove provided on the dome scrap. The chute helps to keep the bottle in the upstanding position with the longitudinal axis of the bottle aligned along the vertical until the dome scrap is contacted by the rotating belts. The belts engage the dome in a groove between two annularly enlarged portions of the dome and serve to both spin the bottle while moving the bottle, in conjunction with the conveyor through the trimming apparatus. A knife is horizontally mounted below the belts at a height that corresponds to a notch provided at the base of the dome scrap. The knife point projects into the neck of the bottle.
As the bottle spins through the trimming apparatus, a razor edge of the knife cuts into the notch to remove the dome scrap from the bottle. The belts are each mounted on a pair of pulley wheels. Each pair of pulley wheels is controlled by a drive means which rotate the belts in a similar counterclockwise direction so that the belts move in opposite directions on the groove in the dome scrap of the bottle. This provides for spinning the bottle because the inner portion of the first belt is moving in a forward direction corresponding to the direction of travel of the conveyor belt moving through the trimming apparatus as the inner portion of the second belt moves in a backwards direction. The first belt is greater in length than the second belt such that the first belt engages the bottle first which pulls the bottle into the trimming apparatus before the second belt makes contact with the bottle. Additionally, the first belt extends further and remains in contact with the bottle after the second belt has lost contact which causes the scrap dome to be carried out of the trimming apparatus. The first belt is rotating at a slightly faster rate than the second belt, which causes the bottle to advance through the trimming apparatus while at the same time spinning on its axis. Preferably, the knife is provided with a heater means. This helps the razor edge melt the plastic material as the knife cuts the dome scrap from the bottle to provide a smooth, clean cut at the top of the bottle.
(2) Prior Art
A spin trimming apparatus using only a single moveable belt is described in U.S. Pat. No. 4,445,406 to Thatcher. This trimming apparatus is comprised of a belt support bar, which supports the moveable belt, and an opposite bottle dome support bar. The belt support bar and the bottle dome support bar are mounted above a conveyor belt, which moves the bottle through the support bars and the trimming apparatus. The bottle dome support bar has a pair of longitudinal grooves that mate with corresponding rim portions on the dome. The rim portions form an intermediate dome groove that is contacted by the moveable belt to spin the bottle along the support bars and through the trimming apparatus. A trimming knife blade is mounted along the length of the bottle dome support bar with the cutting edge of the knife extending progressively inwardly towards the path of the bottle moving along the conveyor, through the trimming apparatus. This provides for cutting the dome from the bottle as the bottle moves down the knife edge. The problem is that the support bar and moveable belt tend to spin the bottle at a slow rate. This necessitates that the knife blade be a relatively long member, extending a substantial distance along the length of the bottle dome support bar.
U.S. Pat. No. 3,429,211 to Pelot describes a similar device where a dome portion is removed by means of a moveable belt that advances the bottle along the cutting edge of an angled knife blade.
U.S. Pat. No. 4,876,930 to Thatcher describes an improved spin trimming apparatus which is capable of positioning the bottle being trimmed in a predetermined orientation with respect to its starting orientation to ready the bottle for a subsequent finishing operation in a production line.
Several prior art trimming apparatus have rotating devices such as a rotating wheel or a turret that rotates a hollow, plastic bottle in an arcuate path past a stationary knife edge to trim dome scrap from the bottle. This type of device is illustrated in U.S. Pat. Nos. 3,675,521 to Ziegler; 3,800,638 to Duikers et al; 3,962,938 to Reilly et al; 3,886,824 to Michel et al and 4,614,018 to Krall U.S. Pat. No. 3,967,516 to Griesing et al describes a trimming apparatus having a rotating wheel that moves the bottle in an arcuate path along a fixed guide while a rotating blade trims the dome scrap from the bottle. These trimmer apparatuses tend to be extremely complicated, which can translate into substantial down time for a production line if a part of the apparatus malfunctions.
Other types of trimming and cutting apparatuses are shown by U.S. Pat. No. 3,541,905 to Mey, which describes a device for radially cutting tubular workpieces to form piston rings or cylinder liner blanks, and the like. U.S. Pat. No. 3,728,063 to Langecker describes an apparatus that removes neck waste from a hollow plastic bottle with a striker operated by a piston-cylinder mechanism. U.S. Pat. No. 3,352,404 to Settembrini is only generally related to the present invention and describes an air-pervious conveyor belt for maintaining a plastic bottle on a conveyor belt in a stable position.
What is needed is a trimmer apparatus for blow molded hollow, plastic bottles that is relatively simple in construction and that uses a belt system to spin the bottles down a longitudinal path through the trimmer apparatus wherein the bottle moves past a knife edge which removes the dome scrap from the bottle.